1. Field of the Invention
This invention relates to new compositions of matter and to a method of controlling plant growth therewith. More particularly, it relates to new thiadiazole ureas and to the control of plant growth, especially of undesirable plants, with the new compounds.
2. Description of the Prior Art
As is well known to those familiar with this art effective control of undesired vegetation governs, to a large degree, yields from food crops. When weeds and other unwanted plants are controlled, one source of competition for the available moisture, nutrients, sunlight and the like is eliminated. Furthermore, effective control also increases the efficiency of maintenance along roadways and railroad tracks, near industrial buildings, along power rights-of-way and the like.
The problems associated with effective control of undesired plants in each of the named areas are quite different. For example, when treating crops, or land which is being prepared for crops, the herbicide chosen should be selective in its activity. That is, it should be able to kill weeds and other unwanted plants, but it must be harmless to the food crop plant growing or to be grown in the treated area. When treating certain other areas such as under power lines, it may be helpful to kill all plant life, and a herbicide which is non-selective will be most useful in this application.
Chemical herbicides are classified generally according to the type of activity possessed thereby. A given compound may possess more than one type of activity depending upon its mode of application and the rate at which it is applied. In addition, herbicides are usually classified as selective or non-selective pre-emergents or post-emergents. The former are applied to the soil before the seeds germinate, and to be effective they must be in intimate contact with the seeds, or with the germinated seedlings. Since weed seeds will germinate closer to the ground than crop seeds, a non-selective pre-emergence herbicide can be effectively used if its penetration is limited to a depth above the crop seeds. Since this is not always possible, the most effective pre-emergence herbicide is one which is selective in its nature. If the selected compound will kill the seed and germinated seedlings of undesirable plants without harm to the seed and germinated seedlings of the crop, there will not be any danger from overpenetration.
Post-emergence herbicides, on the other hand, are applied after the crop and weeds have attained substantial height. Generally speaking, if a compound is found to have post-emergence activity it will not be selective. This is in keeping with the observation that, as a rule, herbicidally active compounds will not be selective in their action on plant life.
The prior art, for example, in an article by S. Giri and H. Singh, J. Indian Chem. Soc., 43 (7), 477-80 (1966), discloses certain 1,3-di-substituted ureas, sulfonylureas and related compounds. Another reference, an article by A. Ermili and I. Cortese, Formaco (Pavio), Ed. Sci., 18 (8), 607-13 (1963), see C. A. 60, 2208c (1964), discloses such compounds as 1-(1,3,4-thiadiazol-2-yl)-3-(p-toluenesulfonyl) urea and 1-(5-methyl-1,3,4-thiadiazol-2-yl)-3-(p-toluenesulfonyl) urea. This art does not disclose herbicidal activity for the compounds taught therein. No art is known which does teach herbicidal activity for the referenced compounds or for the compounds to be more fully described in this application.
The starting materials for many of the compounds embraced in the present invention are 2-amino or alkylamino-5-substituted-1,3,4-thiadiazoles. These starting materials may be prepared in accordance with the method of Lazari and Sharghi, J. of Het. Chem., 3, 336 (1966), or by other known literature methods.